<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
    const p = new Promise((resolve,reject) => {
        //创建对象
        const xhr = new XMLHttpRequest();
        //初始化
        xhr.open("GET", "https://api.apiopen.top/getJoke");
        //发送
        xhr.send();
        //绑定事件，处理响应结果
        xhr.onreadystatechange = function(){
            //判断
            if(xhr.readyState === 4){
                //判断响应状态码  200-299
                if(xhr.status >= 200 && xhr.status < 300){
                    //表示成功
                   resolve(xhr.response);
                }else{
                    //如果失败
                    reject(xhr.status);
                }
            }
        }
    })
    //指定回调
    p.then(function(value){
        console.log(value);
    },function(reason){
        console.error(reason);
    });
    </script>
</body>
</html>